1. Field of the Invention
The present invention relates to thick-film capacitors, more particularly to thick-film-capacitors formed on ceramic substrates.
2. Technical Background
As semiconductor devices such as integrated circuits (IC) operate at higher frequencies, higher data rates and lower voltages, noise in the power and ground (return) lines and supplying sufficient current to accommodate faster circuit switching becomes an increasingly important problem requiring low impedance in the power distribution system. In order to provide low noise and stable power to the IC, impedance in conventional circuits is reduced by use of surface mount technology (SMT) capacitors interconnected in parallel. The higher operating frequencies (higher IC switching speeds) require that voltage response times to the IC be faster. Lower operating voltages require that allowable voltage variations (ripple) and noise are smaller. For example, as a microprocessor IC switches and begins an operation, it calls for power to support the switching circuit. If the response time of the voltage supply is too slow, the microprocessor will experience a voltage drop or power droop that will exceed the allowable ripple voltage and noise margin and the IC will trigger false gates. Additionally, as the IC powers up, a slow response time will result in power overshoot. Power droop and overshoot must be maintained within allowable limits by the use of capacitors that are close enough to the IC that they provide or absorb power within the appropriate response time.
Capacitors for dampening power droop or overshoot are generally placed as close to the IC as possible in order to improve their performance. Conventional designs have capacitors surface mounted on an interconnect substrate and clustered around the IC that is mounted on the same interconnect substrate. In this arrangement, large numbers of capacitors requires complex electrical routing, which leads to increased inductance. As frequencies increase and operating voltages continue to drop, the capacitance must be supplied at increasingly lower inductance levels.